Podocyte Injury in Early Progression and Reversal of Diabetic Nephropathy

The proposed studies follow two critical questions: (1) Does podocyte injury and loss occur in
diabetic patients while they remain normoalbuminuric and do not show GFR decline and if so, can podocyte injury predict early progression of diabetic nephropathy?; (2) Do podocyte recover and regenerate following reversal of diabetic nephropathy after pancreas transplantation? These, so far, unanswered questions can change our current view about the pathophysiology of diabetic nephropathy and may open new horizons for how to prevent progression of the disease in early stages. Answering the second question is also conceptually critical in the evolving field of podocyte regeneration. Our group has unique abilities and resources to tackle these difficult issues. First, we have access to a large archive of longitudinal research kidney biopsies obtained from type 1 diabetic patients through the JDRF funded Natural History Study (NHS) of diabetic nephropathy and the NIH funded Renin Angiotensin System Study (RASS). Sixty-eight NHS patients also completed RASS, providing careful longitudinal renal functional and clinical data and 3 biopsies at baseline, 5 and 10 years. Twenty-two of these patients received placebo in RASS study, among which we will select biopsies for the proposed studies. We will study podocyte injury in 3 longitudinal biopsies from 10/22 patients and will compare those to biopsies from living kidney donors to determine if podocyte injury precedes and/or predicts early diabetic nephropathy. Second, we have access to unique longitudinal biopsies (baseline, 5 and 10 years) from type 1 diabetic patients who underwent successful pancreas transplantation and showed reversal of diabetic nephropathy. In fact, to our knowledge, this is the only human model of documented reversal of diabetic nephropathy which provides a unique opportunity to answer the second question outlined above. We will determine if podocyte injury reverses prior or parallel to the reversal of diabetic nephropathy by studying 11 longitudinal biopsies obtained at baseline, 5 years and 10 years following pancreas transplantation. This will be the first human study to explore relationship between podocyte regeneration and diabetic nephropathy reversal.

Diabetic kidney disease (DKD) is by far the most common cause of end stage kidney disease in the US. Novel insights about the evolution of DKD lesions may help identify new targets for treatment. Most of what we currently know about the structural changes of DKD comes from the studies performed by two-dimensional (2D) transmission electron microscopy (TEM); however, complexity of some of the cellular and subcellular structures demands for 3D studies. Here, we propose to apply serial block face scanning EM (SBF-SEM), a relatively novel technique that allows for 3D EM studies, to study DKD in human and mice. We will optimize SBFSEM tissue preparation protocols, will generate 3D models to better understand the spatial relationships between the glomerular structures. Adding quantitative approached to the volumetric data from SBF-SEM will make this much more powerful. We will develop quantitative approaches to study mitochondrial number and fission/fusion and subpodocyte space volume. Accomplishment of these goals may help finding structural evidence of pathogenetic processes that may be amenable to interventions. These could lead to proof of concept studies where interventions altering these structural variables influence outcomes.

The DiaComp Steering Committee is the governing body of the consortium. The principle function of this committee is to guide the scientific direction of the consortium. This is accomplished by creating various subcommittees necessary to advance the scientific goals and providing guidance to the broader complications research community. Policies for the consortium are developed through consultation with the External Evaluation Committee